Pydantic

Suppose you want to use pydantic to manage your validation logic instead of Cyclopts. Pydantic offers a validate_call() decorator that performs validation checks on invocation.

from cyclopts import App
from pydantic import validate_call, PositiveInt

app = App()


@app.command
@validate_call
def foo(value: PositiveInt):
    print(value)


app()

$ python my-script.py foo 10
10
$ python my-script.py foo -1
╭─ Error ────────────────────────────────────────────────────────────╮
│ 1 validation error for foo                                         │
│ 0                                                                  │
│   Input should be greater than 0 [type=greater_than,               │
│ input_value=-1, input_type=int]                                    │
│     For further information visit                                  │
│ https://errors.pydantic.dev/2.5/v/greater_than                     │
╰────────────────────────────────────────────────────────────────────╯

A benefit of this approach is that calling your decorated function from python code will still perform these validation checks. Pydantic's types are aliases for Annotated[python_type, additional_metadata], so they are naturally compatible with Cyclopts.